1. Field of the Invention
This invention relates to coating compositions and methods for treating reinforcement fibers. The invention includes preparing the coating compositions, applying the coating compositions to form treated reinforcement fibers and, employing the treated reinforcement fibers in asphalt and portland cement concrete materials. The treated reinforcement fibers provide advantages as compared to non-treated reinforcement fibers including, but not limited to, improved adhesion between the treated reinforcement fibers and, between the treated reinforcement fibers and asphalt and portland cement concrete.
2. Background of the Invention
Reinforcement components, such as fibers, are generally known in the art. Further, addition of these reinforcement components to building materials, such as concrete, including asphalt and portland cement concrete and the like, is known to add strength, toughness, and durability to improve the integrity of the material properties of the concrete. For example, a reinforcement component is typically added to concrete to reduce the effect of two main structural deficiencies: 1) low tensile strength and 2) low strain at fracture. The tensile strength of concrete is relatively low because concrete, when formed, normally contains numerous micro-cracks. It is the rapid propagation of these micro-cracks under applied stress that is responsible for the low tensile strength of the material.
Known reinforcement components include, for example, various gauges of wire mesh or reinforcement fibers, such as, asbestos fibers, glass fibers, steel fibers, mineral fibers, natural fibers, synthetic fibers (such as polymer and aramid fibers), and cellulose fibers. Some reinforcement fibers are better suited for particular applications than others. There are disadvantages associated with these known reinforcement components. For example, they generally do not exhibit good adhesion to concrete. Exposure of these reinforcement components to various environmental conditions, such as alkaline media, can cause the reinforcement components to degrade. Some advances have been made in the area of reinforcement components to provide improved adhesion. For example, additive solutions can be added to fiber/concrete mixtures to improve adhesion. However, even with the additive solutions, reinforcement fibers still have disadvantages that weaken or, otherwise, limit their effectiveness.
Furthermore, it is generally known that surface properties of shaped articles such as polymeric films and fibers can be modified by a graft polymerization process. In this process, the article is treated with a free radical generating agent, such as organic peroxide or high energy radiation and then, contacted with an ethylenically unsaturated monomeric material under conditions wherein the monomer or graft polymer chain is covalently bonded to the substrate of the article.
There are, however, disadvantages associated with conventional graft polymerization processes. For example, films formed by these processes can be prone to delamination under certain conditions. In order to improve the integrity of a film deposited on a surface of a substrate, the substrate may be treated to grow a polymer coating using a chemical grafting process. The resulting coating is covalently bonded to the substrate and is resistant to delamination. Chemical grafting involves the activation of the substrate. The substrate is activated which causes chains of monomers linked by carbon-carbon bonds to grow on the substrate. The growth has been characterized as “whiskers”. These whiskers can impart desirable properties to the substrate without imparting negative properties to the substrate.
In general, a substrate material possesses certain hydrogen atoms which are more active than the “bulk hydrogen atoms” in the material. Examples of relatively more active hydrogen atoms include the tertiary hydrogen in polypropylene, the amide hydrogen in proteins, and the hydroxyl hydrogen in polysaccharide. The chemical grafting process uses graft initiators which have the capacity to remove the active hydrogen atoms and initiate the growth of polymer chains at the site of the removed hydrogen atoms. This process results in a covalent bond formed between the grafted polymer and the substrate. Further, the process can result in a coating or film chemically grafted, i.e. , covalently bonded to the substrate.
Accordingly, there is a need for reinforcement fibers that impart improved structural properties to building materials to which they are added and, in particular, the need exists for treated reinforcement fibers having a coating or film chemically applied thereto such that when the treated reinforcement fibers are added to concrete materials, the result is improved adhesion between the fibers and improved adhesion to the concrete, as compared to untreated reinforcement fibers known in the art. Further, it is desired that application of the coating or film can be carried out with minimal surface preparation of the reinforcement fibers and can result in a relatively thin coating layer on the surface thereof.